Petroleum asphalts are widely used in road pavement materials, emulsions, vibration damping materials and the like. According to statistical data on demand and supply of petroleum asphalts in a journal from The Japan Asphalt Association and according to a petroleum statistical estimate by the Japanese Ministry of Economy, Trade and Industry (the former Ministry of International Trade and Industry), the demand and supply of petroleum asphalts in Japan were balanced both at more than 6,000,000 tons until around 1998. However, the demand and supply have both decreased below 6,000,000 tons since around 2000, and the data has shown an oversupply trend. In 2007, the supply stood at a little over 5,000,000 tons whereas the demand showed a sharp decline to slightly more than 3,000,000 tons. Thus, excess supply is increasing.
The excess supply is expected to continue. With soaring prices of petroleum products these days, it is demanded that the applications of petroleum asphalts be increased. Of the petroleum asphalts, straight asphalts are stably inexpensive materials. According to prices of construction material and wages by Construction Research Institute Japan, the straight asphalts are traded in the market at approximately 60,000 yen per tank truck load (approximately 6 yen per kg), and the freight costs as little as the materials. The straight asphalts are quite inexpensive materials.
The straight asphalts are composed of malthene (petrolene) that is soluble in normal pentane, and asphaltene that is insoluble in normal pentane. The malthene has a resin component and an oil component. It is assumed that the straight asphalt has a structure in which asphaltene coated with the malthene resin component is colloidally suspended in the malthene oil component. Although the exact chemical structure of the straight asphalt is not established yet because it is a natural material (a high-boiling fraction obtained in petroleum refining), the chemical composition is assumed to be a complex of the various aliphatic hydrocarbon compounds.
The straight asphalt is generally solid at normal temperature. The straight asphalt is used as road pavement materials, mixtures, emulsions, vibration damping materials and the like (Patent Document 1). However, the cured products have poor storage stability, heat resistance, water resistance, and mechanical strength such as hardness.
With respect to these problems, it is proposed that modifiers are used to improve the above properties of the straight asphalts. Known modifiers for drainage pavement asphalts include graft-modified polymers of ethylene/vinyl acetate copolymer, ethylene/acrylic acid copolymer or ethylene/conjugated diene copolymer with an unsaturated dicarboxylic acid; graft-modified polymers of polyethylene or polypropylene with an unsaturated dicarboxylic acid; polymer alloy compounds such as block copolymers obtained by IPN (interpenetrating polymer network) methods; and styrene/conjugated diene copolymers (Patent Documents 1 to 4).
Patent Document 5 describes a modified asphalt mixture obtained by mixing a straight asphalt with a reactive solvent that contains a bisphenol A epoxy resin and a modified aliphatic amine which both have compatibility with the asphalt. It is described that the viscosity increase is excellently prevented in the production and placement processes and the mixture can give pavements with a desired strength.
However, the modified straight asphalts obtained with the above modifiers have poor storage stability over long periods.
It is also known that straight asphalts are modified with epoxy resins or urethane resins. However, the straight asphalts are non-polar materials and show bad compatibility with polar materials such as epoxy resins and urethane resins, resulting in separation. Thus, homogeneous and rigid cured products cannot be obtained. This problem is due to the fact that the straight asphalt is a complex of the various aliphatic hydrocarbon compounds and is a non-polar material with no molecular charges, similar to water and oil being immiscible with each other.
As described above, it is difficult that the straight asphalts are used in general chemical products ranging widely from adhesives and coating materials to floor materials and waterproof materials that contain general synthetic polar resins such as urethane resins or epoxy resins. Thus, the applications of the straight asphalts are limited to composites and emulsions as road pavement materials.
To address these problems, asphalt/polyol emulsions are obtained by mixing and emulsifying an asphalt, a polyol, a surfactant having HLB of about 13 to 18, and a plasticizer. Such modified asphalts are improved in compatibility with polar materials (Patent Document 6). The patent document describes that with the improved compatibility between asphalt and polyol, the asphalt/polyol emulsion together with a reacting agent such as an isocyanate can give urethane asphalts used as waterproof materials, floor materials and other various industrial materials.    Patent Document 1: JP-A-2000-239527    Patent Document 2: JP-A-S61-152764    Patent Document 3: JP-A-2002-020626    Patent Document 4: JP-A-2006-143954    Patent Document 5: JP-A-H07-118541    Patent Document 6: JP-A-S62-218448